Rotating anode x-ray tube

ABSTRACT

In an exemplary embodiment, the shaft for the rotating anode is supported by ball bearings in a tubular support-mounting extending into the envelope of the tube. Particularly in the case of rotating anodes, which rotate very rapidly (e.g. 300 Hz), it is disadvantageous that rubbed-off residue falls out of the bearings, on the one hand, and that lubricant leaves the bearings, on the other hand. For the improvement of the operating properties and a permanent lubrication, and the improvement of the high voltage strength by avoidance of loose particles in the tube envelope, the disclosure provides an arrangement of covers on the bearings and possibly one or more radial barriers rotating with the shaft between the stationary covering parts. A rotating anode x-ray tube with a bearing protected in accordance with the disclosure is particularly suited for use in x-ray tubes with very rapidly rotating anode plates.

BACKGROUND OF THE INVENTION

The invention relates to a rotating anode x-ray tube wherein the anodeshaft is supported by ball bearings which contain a lubricant, and acover is provided for the purpose of keeping the lubricant in thebearing. Rotating anodes of this type are, for example, known from theBritish Patent No. 1,247,316.

In the known x-ray tubes great demands are made of the bearings becausethey run in high vacuum under temperature variation stresses. Therefore,in the case of bearings which must run in this manner for a long periodof time without relubrication, in the construction known according tothe abovecited reference, friction surfaces of a material capable ofbeing lubricated have been manufactured. However, the danger here isthat the lubricant forms a rubbed (or worn)-off residue which falls outof the bearing. Other lubricants introduced in the bearing in a knownfashion, such as molybdenum sulfide and silver, etc., can likewiseescape from the bearing causing an impairment of the lubrication of thelatter.

In an x-ray tube according to the U.S. Pat. No. 2,280,886, in anembodiment, the ball bearings are provided with sealing parts which havethe purpose of providing chambers for accommodating molybdenum sulfideas lubricant. However, bearings of this type with an encased (enclosed)ball race (or running) space have not proven successful in x-raytechnology because, due to the large radial clearance necessary in orderto absorb the temperature expansion, a gap must remain which is so widethat lubricant particles can escape and enter the tube-space.

Another x-ray tube, known according to the U.S. Pat. No. 2,570,770, hasa bearing in proximity of the anode to which there is pre- (or series-)connected, on the side facing the plate, a receptacle with soft materialas lubricant. The receptacle is to be mounted on the shaft. However,such a design has not proven successful because in the case of x-raytubes the disadvantage arises that the receptacle co-rotates andlubricant particles can be spun (or centrifuged) into the tube space.

SUMMARY OF THE INVENTION

Accordingly, the object underlying the invention resides in providingmeasures, in the case of a rotating anode x-ray tube with lubricatedball bearings, to keep the lubricant on the bearing and to avoid thefalling-out of rubbed-off residues, on the other hand. In accordancewith the invention, this object is achieved by the features disclosed inclaim 1.

Through the utilizaton of a ball bearing in which the inner races of theballs are associated with the rotating axis, and the exterior races areassociated with a tubular support-mounting, loose particles occurringduring rotation are spun (or centrifuged) outwardly, so that cover metalsheets, which are annular and connected with the tubularsupport-mounting at their outer margin, prevent rubbed-off residue andlubricant present in loose form from leaving the bearing. The lubricantcover configuration for the bearing proximate to the anode plate canhave the form of a metal sheet which is arranged on the side of suchproximate bearing which is adjacent the anode plate. The gap remainingbetween the interior edge of this metal cover sheet and the shaft isexpediently kept on the order of magnitude of the radial slack (orclearance), in order to allow loose particles as little opportunity aspossible for escaping from the bearing into the tube; i.e., on such anorder of magnitude which results from the radial clearance necessary forthe running of the bearing, the tolerances to be allowed for themanufacture, and the center deviation remaining during the centering. Inthe case of a 10 mm-thick shaft consisting of hardenable steel this isan air gap +0.2 to +0.265 mm. Toward the other side of the proximatebearing a contamination of the tube interior space is avoided anyway ifthe bearings are arranged in a sealed tubular support separated from theinterior space of the x-ray tube.

Through an additional metal sheet on the side of the proximate bearingnot facing the anode plate, lubricant can be fixed on the bearing intowhich it is filled. Correspondingly, longer lasting lubrication can alsobe obtained on the anode-remote bearing.

In particular, on the side of the proximate bearing facing the anodeplate, it has proven to be favorable to provide a bearing covering inthe form of a grooved ring including an outer axially extended annulusadjacent the exterior bearing race, a radially extending web leadinginwardly toward the shaft, and a reversely extending flange disposed inencircling relation to the shaft. In this manner, a lubricant barrierwith a collecting (or trapping) space or recess is obtained in whichloose particles can be retained. Also in the case of this arrangement,the clearance between the interior side of the flange and the exteriorside of the shaft is expediently on the order of magnitude of therequired bearing slack (or clearance). In particular on account of thereversely axially extending flange arranged in this manner an extended(or elongated) narrow path along the shaft and hence an improvedretention of loose particles can be achieved.

It has also proven to be favorable to provide lubricant barrierconfigurations both in the form of a cover sheet and in the form of arecessed ring. This is very particularly advantageous if, in addition,the shaft is provided with a thickening constructed in a step-wisefashion, whereby the step lies between the sheet and the end of thereversely extending flange of the recessed ring. The height of the stepshould be at least 0.7 mm and, on account of the axial play (which maybe a maximum of 0.3 mm with a radial clearance of thirty microns, 30 μ)should not exceed an order of magnitude of one millimeter (1 mm). Inutilizing a sheet whose inner diameter is so selected that the distancefrom the adjoining exterior surface of the shaft, which is before thestep, corresponds at least approximately to the bearing clearance, thisleads to the result that passing-through particles reach the step andare spun (or centrifuged) by the latter into the collector recess of thering on account of the rotation of the shaft. Thus, the direct travel(or migration) path along the shaft is cut off for the particles.Between the step and the collector recess of the ring additional stepsand coverings, designed in a corresponding fashion, can be arranged inorder to increase the effect.

Further advantages and details of the invention shall be explained inthe following on the basis of the exemplary embodiments illustrated inthe Figures on the accompanying drawing sheet; and other objects,features and advantages will be apparent from this detailed disclosureand from the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In FIG. 1 an x-ray tube, partially in section, is illustrated providedwith an inventively improved mounting for the rotating anode thereof;

In FIG. 2 a partial sectional view of the bearing which is in proximityto the anode plate is illustrated;

In FIG. 3 a design with increased effectiveness is illustrated; and

In FIG. 4 a modified solution is illustrated.

DETAILED DESCRIPTION

In FIG. 1, reference numeral 1 designates a rotating anode which ishoused in a glass vacuum envelope 2. Moreover, the envelope 2additionally contains, in a manner known per se, a cathode 3. The anode,with the envelope 2, is sealed onto a tubular part 5, the so-calledanode stem, via a collar 4. Between the anode 1 and the support-mounting5, ball bearings 6 and 7 are disposed. The rotating anode 1 itselfconsists of an anode plate 8 which is fixedly secured at the upper endof a shaft 9. Also disposed on the shaft is a rotor 10 which may bedriven via a stator to be exteriorly joined to the envelope 2, and notillustrated, to effect rotation of the anode plate 8.

The two ball bearings 6 and 7 are disposed within the rotor 10 and, withtheir exterior races 13 and 14, are mounted on the interior side of thetubular support-mounting 5. The rolling bearing is provided in a mannerknown per se, by balls 15 which are supported in a ball cage 16. Theballs 15 of the bearing 6, in proximity to the anode plate, thus rundirectly on the shaft 9, whereas for the balls 15 of the bearing 7,which is remote from the anode plate, a race 17 with a race (or running)channel is provided on the shaft 9 in order to prevent longitudinaldisplacement of the shaft.

At the plate-side end of the proximate bearing 6 a cover metal sheet 18is provided which is fixedly clamped at its exterior edge between therace 13 and the channel-shaped ring 19, FIG. 2, by being disposedbetween the lower axial end of the outer annulus 20 of the ring 19 andthe bearing race 13. The channel-shaped ring 19, moreover, consists of apart 21, extending radially toward the shaft 9 at the other axial end ofthe annular part 20, and of a radially inner flange 22 extending axiallyin surrounding relation to the shaft. In this manner, the annular recess23 is obtained, which is formed by the interior borders of the annuluspart 20, the radial part 21, and the reversely extending flange 22,which recess 23 is well-suited for collecting loose particles whichovercome the barrier formed by sheet 18 and pass through the gap betweenthe interior edge of the sheet 18 and the shaft 9. This gap, just likethat between the flange 22 and the thickened part 24 of the shaft 9, maycorrespond in size to the necessary bearing slack (or clearance).

A further improvement in the seal is obtained by a step 25 which isdisposed between the thickened part 24 and the normal part of the shaft9. The latter is so arranged that it is disposed between the uppersurface of the covering 18 and the lower edge of the flange 22 (asviewing in FIG. 2). In this manner, particles, which overcome thebarrier provided by sheet 18 by passing through the gap at its inneredge, are centrifuged, or flung toward the exterior at the step orshoulder 25 and into the recess 23 of the channel-shaped part 19, onaccount of the rotational movement of the shaft 9, and said particlesare retained therein. The entire arrangement is wedged peened-over bymeans of a closing device at 26 such that a fixation of the parts 18 and19 together with the bearing 6 is achieved. Possibly a covering 18',indicated in broken lines at the underside of the bearing 6, can yetadditionally be fixedly clamped in order to retain lubricant on thebearing.

In a similar manner as bearing 6, bearing 7 can also be provided withcovering sheets corresponding to coverings 18, 18', FIG. 2. For thelatter, in particular, only coverings corresponding to 18 and 18' are tobe provided, because from this bearing 7 no loose particles can reachthe interior space of the envelope 2. Through such a covering of bothbearings 6 and 7 it has been shown that it is possible to achieve anincrease in life by 300%, with permanently reduced running (orbackground) noise, in particular, for very rapidly running anodes.

The effect can be increased by a multiple layout of the combination ofsheet 18 and step 25. In FIG. 3, such a layout is indicated in which,through insertion of a sheet 18" and a step 25' between the sheet 18 andthe end of the bearing 6, the combination is doubled with the creationof an additional collecting space 23'. For the purpose ofsupport-mounting a spacing ring 20' is inserted, and an additionallythickened part 24' results on the shaft 9.

The steps 25 and 25' can, as illustrated in FIG. 3, be obtained throughprocessing of the shaft 9. However, as indicated by broken lines 29 and30 in FIG. 2, they can also be manufactured by means of a ring 31, FIG.4, which is mounted on the shaft 9 such that it forms the thickening 24and its one end face represents the step 25. The ring can, for example,be soldered-on or welded-on, etc.

In FIG. 4 this design is illustrated in a partial section, whereby alsothe step 25' is designed as a ring 31'. Expediently the same materialwill be used for shaft 9 and rings 31, 31', or at least materials havingvery similar coefficients of expansion will be used.

Otherwise, the tube can be put in operation in a conventional manner byconnecting corresponding voltages between the leads 27 and the tubularsupport-mounting 5 functioning as the anode stem. To this end, electronsissuing from the support structure 28 of a thermionic cathode arrive onthe focal spot path of the anode plate 8 and there produce x-rays.

It will be apparent that many modifications and variations may beeffected without departing from the scope of the novel concepts andteachings of the present invention.

I claim as my invention:
 1. A rotating anode x-ray tube comprising an x-ray tube envelope (2), a rotating anode plate (8) in the envelope, a rotatable shaft (9) supporting said anode plate for rotating, a ball bearing assembly for rotatably mounting said shaft (9) comprising a remote bearing (7) remote from the anode plate having an interior race (17) on the exterior side of the shaft (9), and a proximate bearing (6) in proximity to the anode plate (8) having an exterior race (13) fixedly arranged relative to the envelope (2), and bearing cover means for keeping the lubricant in the bearing, said bearing cover means comprising an annular bearing cover configuration (18, 19) fixedly connected with said exterior race (13) and extending radially inwardly at the side of the proximate bearing toward said anode plate (8) to provide in conjunction with the centrifugal force on the lubricant during operation, a barrier to migration of lubricant in an axial direction toward said anode plate, characterized in that a step (25) at a thickening of the shaft (9) in directin of the plate (8), is additionally provided, and characterized in that the annular bearing cover configuration comprises a sheet metal ring (18) extending from the side of said exterior race (13) which is toward said anode plate (8), and extending radially inwardly to provide an inner edge encircling said shaft on the side of said step (25) remote from said anode plate, said annular bearing cover configuration further comprising a channel shaped annular part (19) including collecton means (23) on the side of said step toward the anode plate.
 2. A rotating anode x-ray tube according to claim 1, characterized in that, between the collector means (23) of the annular part (19) and the proximate bearing (6), additional steps (25') and metal sheets (18") are arranged as barriers to migration of lubricant to the interior of the envelope. 